The invention relates to processes for the preparation of free-flowing end products of strongly acidic cation exchangers prepared according to Patent Application 19548 012.0 (=U.S. Pat. No. 6,228,896).
Strongly acidic cation exchangers prepared by the processes of the publications cited in Patent Application P 19 48 012.0 (=U.S. Pat. No. 6,228,896) with and without the use of inert swelling agents, as well as the strongly acidic cation exchangers prepared by the process according to the invention and of the patent application mentioned, have the disadvantageous property that the cation exchanger dewatered in a filter at the end of the preparation process are not sufficiently free-flowing for industrial handling, further processing and use.
EP 0 009 395 discloses the addition of wetting agents and water-soluble initiators in the polymerization stage. With the aid of the additions, the formation of an emulsion of extremely fine-particled ion exchangers, particle size 0.01-1.5 xcexcm, is achieved but the surface charge of coarse particles in the anhydrous state is not influenced in such a way that they become free-flowing as bulk material. The treatment of sulphonated styrene/divinylbenzene copolymer with water is part of the preparation process described in EP 0 009 395 for cation exchangers. The end products thus prepared are not free-flowing.
EP 0 223 596 A 2 describes the hydration of the sulphonated product containing sulphuric acid in the process for the preparation of a cation exchanger.
However, the treatment of the sulphonated cation exchanger with water in this process stage does not result in the free flowability of the end product. The relevant technical literature proposes no solutions for eliminating these disadvantageous properties of the particle beads of strongly acidic cation exchangers.
It is the object of the invention to influence the preparation process of strongly acidic cation exchangers by suitable additions of substances and/or process engineering measures so that the particle beads of the end products are free-flowing.
It has now been found that free-flowing strongly acidic cation exchangers can be prepared by means of additions of substances and process engineering measures in the polymerization stage or after the filtration of the end product. Specifically, these are subsequent procedures according to the invention which lead to a substance known per se and having novel properties:
1. Free-flowing end products are obtained if the preparation of the starting material for the strongly acidic cation exchanger, the styrene/divinylbenzene copolymer is influenced in such a way that a higher proportion of emulsion polymer forms. This is achieved, according to the invention, by adding
wetting agents, e.g. sodium salts of alkanesulphonic acids having a chain length C12-C18 in a concentration of up to 0.25 g/l of water or
0.05 to 0.20 g/l of water of a water-soluble initiator, such as, for example, potassium peroxydisulphate (K2S2O8)
xe2x80x83to the batch of the copolymerization system 20 to 120 min after reaching the gel point.
Strongly acidic cation exchangers prepared according to Examples 1 and 2 are permanently free-flowing.
2. Free-flowing end products are also obtained if the non-free-flowing strongly acidic cation exchangers prepared by the procedure cited are treated with surface-active substances, such as nonionic surfactants, as prepared by an addition reaction of ethylene oxide and propylene oxide with natural fatty alcohols having a chain length C12-C14, or
xe2x80x83alkylphenol polyethylene glycol ethers or cationic and amphoteric surfactants or emulsifiers of the fatty alcohol polyalkylene glycol ether type or anionic surfactants of the paraffinsulphonate type.
If the strongly acidic cation exchanger is used in the food industry (e.g. drinking water preparation), the surface-active substance must be suitable as an additive for food. Sorbitan fatty acid esters and polyoxyethylene(20) sorbitan fatty acid esters may be used for this purpose.
According to the invention, this is achieved by treating the end products dewatered in a filter at the end of the preparation process, in a downstream batch or column process, with an aqueous solution which contains a surface-active substance or a mixture of surface-active substances in amounts of 0.1 to 5 g/l of resin. The products are then dewatered and dispatched. The free flowability produced here is temporary and eliminated again by washing with water. Such free-flowing strongly acidic cation exchangers can be prepared according to Examples 3 and 4.
3. Free-flowing strongly acidic cation exchangers are furthermore obtained by subjecting the end products, the non-free-flowing strongly acidic cation exchangers, to a hot water wash which simultaneously purifies the end products and utilizes the heat content of the end products for its superficial drying. According to the invention, the desired effect is achieved by treating the non-free-flowing strongly acidic cation exchangers with hot water at a temperature equal to or higher than 60xc2x0 C. for at least 1 hour, not more than 4 hours, and drying the said cation exchangers after removal of the water utilizing the product heat. By passing through air- or nitrogen, the removal of moisture is accelerated, the residual moisture content is reduced and the free-flowing state of the strongly acidic cation exchanger is reached earlier.
Strongly acidic cation exchangers prepared according to Examples 5 to 7 are temporarily free-flowing.
To evaluate the free flowability, the efflux characteristic from a defined funnel was determined. The dimensions of the funnel are shown in the attached drawing sheet.
The material of the funnel, each having the same internal dimensions, consisted
a) of Teflon and
b) of C2A stainless steel.
The sample material is filled loosely into the funnel.
The outlet orifice of the funnel is closed.
To carry out the flow test, the funnel outlet is opened without vibration.
The flowability of the strongly acidic cation exchangers is assessed according to the following criteria:
1. Total material flows by itself out of the funnel
2. Only the lower part of the funnel flows out spontaneously, and the complete content as a result of lightly tapping the funnel
3. The lower part of the funnel flows out spontaneously; the sample material remains in the upper part of the funnel even with intensive tapping
4. The lower part of the funnel flows out of the funnel only after intensive tapping
5. No material at all flows out of the funnel, not even with tapping.
End products having the rating 1 are classified as xe2x80x9cfree-flowingxe2x80x9d. Since the funnel material considerably influences the efflux behaviour of the end products, the abovementioned evaluations must be carried out in both funnels.
Using the processes according to the invention, the disadvantages associated with the end products are overcome and the following advantageous properties and effects achieved.
The products are free-flowing
The free flowability does not give rise to any technical problem in packaging in the production unit.
No metering problems into small containers at the customer""s premises
An additional purification of the product occurs during the hot washing/separation/drying variant
The additions of substances to the copolymerization system have the advantage that an after-treatment of the end products after the filtration is dispensed with.